Technical Field
The present invention relates to an iron-based sintered alloy for a sliding member that is suitably used for a bearing in which high surface pressure is loaded on an inner circumference surface, and relates to a production method therefor. In particular, the present invention relates to an iron-based sintered alloy for a sliding member, which improves seizure resistance.
Background Art
For example, in sliding members having sliding surfaces to be applied with high surface pressure, such as driving portions and sliding portions of vehicles, machine tools, or industrial machines, etc., a carbon steel which was cut and was quench hardened and tempered, or a sintered alloy, is used. Specifically, since the sintered alloys can have self-lubricating characteristics by lubricating oil infiltrated thereinto, they have superior seizure resistance and wear resistance and are thereby widely used. For example, a bearing is disclosed in Japanese Patent Application Laid-open Publication No. 11-117940. The bearing has a sliding surface provided with an iron-based sintered alloy layer consisting of 10 to 30 weight % of Cu and the balance of Fe.
In addition, an iron-based sintered alloy for a sliding member is disclosed in Japanese Patent Application Laid-open Publication No. 2009-155696. The iron-based sintered alloy consists of, by mass %, 0.6 to 1.2% of C, 3.5 to 9.0% of Cu, 0.6 to 2.2% of Mn, 0.4 to 1.3% of S, and the balance of Fe and inevitable impurities. The iron-based sintered alloy has a structure in which 1.0 to 3.5 mass % of a MnS phase and at least one of a free Cu phase and a free Cu—Fe alloy phase are dispersed in a martensite matrix.
In recent years, for sliding members having sliding surfaces that will be subjected to high surface pressures, further improvement of seizure resistance is required.
In view of this, in the invention disclosed in Japanese Patent Application Laid-open Publication No. 2009-155696, 1.0 to 3.5 mass % of the MnS phase is dispersed. Thus, the decrease of the wear resistance and the increase of the wear characteristics with respect to a mating member due to decrease in the amount of Cu are avoided. However, MnS powder added to a raw powder remain as a MnS phase, whereby dispersing positions of the MnS phase are limited to the pore interior and powder grain boundary. Therefore, an improving effect of the seizure resistance is insufficient. In addition, the MnS powder is stable and does not react with an iron-based matrix, whereby it has low fixability with respect to the matrix and may be exfoliated during sliding.